SOLVENT CHARACTERISTICS IN THE SPECTRAL BEHAVIOR OF ERIOCHROME-BLACK-T

The visible electronic spectral behaviour of Eriochrome Black T, in a number of organic solvents of different characteristics has been exami ned. It was concluded that the dye exists in solution in basic solvent s (based on their autoprotolysis constant, pK(s)) in an azo reversible arrow hydrazone tautomeric equilibrium, while in acetone, acetonitril e and DMSO it exists mainly in the azo form. In DMF and other basic so lvent solutions, the dye exhibits an acid-base equilibrium of the type H2In- reversible arrow HIn2- + H-2. The proportional concentration of the base form (HIn2-), as well as the relative tautomerisation, are l argely dependent upon the concentration of Erio T, the basicity of the solvent and the tendency of the base and/or the hydrazone form to be stabilized by H-bonding interaction with the solvent molecules. The co mpound wasfound to aggr-egate in wafer and hydroxylic solvents. The ba nds displayed by the difSerents forms of the compound have been assign ed to an electronic transition involving the whole molecule with an ap preciable clzalge transfer character.